This invention relates to medical devices for performing diagnostic, mapping, ablative, and other procedures and, more particularly, to a medical device for incrementally moving an electrode a predetermined distance upon each actuation of the device.
The human heart is a very complex organ, which relies on both muscle contraction and electrical impulses to properly function. The electrical impulses travel through the heart walls, first through the atria, and then through the ventricles, with those impulses causing the corresponding muscle tissue in the atria and ventricles to contract. Thus, the atria contract first, followed by the ventricles. This order is essential for proper functioning of the heart.
Over time, the electrical impulses traveling through the heart can begin to travel in improper directions, thereby causing the heart chambers to contract at improper times. Such a condition is generally termed a cardiac arrhythmia, and can take many different forms. When the chambers contract at improper times, the amount of blood pumped by the heart decreases, which can result in premature death of the person.
Non-surgical procedures, for example, management with drugs, are favored in the treatment of cardiac arrhythmias. However, some arrhythmias are not treatable with drugs. For example, drug therapy to combat certain types of cardiac arrhythmias has been found to be successful in only 30 to 50 percent of patients. Because of this low success rate, another conventional remedy is to perform a surgical procedure. According to these procedures, various incisions are made in the heart to block conduction pathways in an effort to abolish the arrhythmia.
More recently, minimally invasive techniques have been developed which are used to locate cardiac regions responsible for the cardiac arrhythmia and to disable the short-circuit function of these areas. According to these techniques, electrical energy is applied to a portion of the heart tissue to ablate that tissue and produce scars which interrupt the reentrant conduction pathways. The regions to be ablated are typically first determined by endocardial mapping techniques. Mapping involves percutaneously introducing a catheter having one or more electrodes into the patient, passing the catheter through a blood vessel (e.g. the femoral vein or aorta) and into an endocardial site (e.g., the atrium or ventricle of the heart), and inducing a tachycardia so that a continuous, simultaneous recording can be made with a multichannel recorder at each of several different endocardial positions. When a tachycardia focus is located, as indicated in the electrocardiogram recording, its position is marked so that cardiac arrhythmias at the located site can be ablated. An ablation catheter with one or more electrodes can then transmit electrical energy to the tissue adjacent the electrode to create a lesion in the tissue. One or more suitably positioned lesions will typically create a region of necrotic tissue which serves to disable the propagation to the errant impulse caused by the tachycardia focus.
Ablation is carried out by applying energy to the catheter electrodes once the electrodes are in contact with the cardiac tissue. The energy can be, for example, RF, DC, ultrasound, microwave, or laser radiation. When RF energy is delivered between the distal tip of a standard electrode catheter and a backplate, there is a localized RF heating effect. This creates a well-defined, discrete lesion slightly larger than the surface area of the electrode (i.e., the xe2x80x9cdamage rangexe2x80x9d for the electrode), and also causes the temperature of the tissue in contact with the electrode to rise.
It has been found that to overcome certain cardiac arrhythmias, it is often necessary to create a relatively long, continuous lesion (i.e., a linear lesion) in the patient""s heart tissue. Conventional techniques include applying multiple point sources in an effort to create a long and continuous lesion. Such a technique is relatively involved, and requires significant skill and attention from the clinician performing the procedure.
Another conventional ablation procedure for creating linear lesions is commonly referred to as a xe2x80x9cdragxe2x80x9d method. According to that method, an ablation catheter carrying one or more ablation electrodes is manipulated through a patient""s blood vessels and to a desired location within the patient""s heart. One or more of the electrodes is manipulated into contact with the heart tissue. Ablation energy is then delivered through the electrode(s) and into the tissue to create a lesion, which is typically slightly larger than the surface area of the electrode contacting the tissue (the electrode""s damage range). After the electrode has been disposed in that location for a sufficient time to ablate the adjacent tissue, the clinician then manually moves the catheter a selected amount by pulling on the catheter shaft, and ablation energy is again delivered to the electrode(s) to ablate the tissue that is then adjacent to the electrode. By continuing this procedure, the clinician attempts to create a continuous, linear lesion to block an aberrant pathway.
However, to create a continuous lesion, the clinician must be careful not to move the catheter too far between successive ablations. If the clinician should accidentally move the catheter too far, then the lesion created will not be continuous, and the aberrant pathway may not be destroyed, requiring that the patient undergo yet another surgical procedure.
Accordingly, it will be apparent that there continues to be a need for a device for performing ablations which ensures the creation of linear lesions, by automatically displacing an ablation electrode in successive, incremental, movements of a predetermined, known distance. In addition, the need exists for a device which moves an electrode in known increments for use in performing other medical procedures. The instant invention addresses these needs.
According to one aspect of the invention, an electrode is slidably mounted over a tubular shaft, for example, a catheter shaft. The electrode is connected to one end of a displacement member, such as a mandrel, stiff wire, or the like. The displacement member may extend through the inside of the catheter shaft and connect to the electrode through a slot formed in the shaft, or may extend along the outside of the catheter shaft to connect to one end of the electrode. The displacement member includes a second end that is connected to a control mechanism which may be manipulated by a user to advance and/or retract the displacement member in controlled, known increments. In this manner, the electrode is incrementally displaced in successive, predetermined distances, and is suitable for use in ablative procedures to create long, continuous lesions.
Thus, in one illustrative embodiment, the present invention is directed to a medical device comprising an elongated, tubular shaft, an electrode slidably mounted over the shaft, an elongated displacement member connected to the electrode, and a control mechanism connected to the displacement member and operative to displace the displacement member in predetermined, incremental amounts to displace the electrode in the incremental amounts.
In another illustrative embodiment, the invention is directed to a method of performing a medical procedure, comprising the following steps: positioning an ablation electrode at a selected site within a patient, the ablation electrode having predetermined dimensions; delivering ablation energy to the electrode to ablate the patient""s tissue disposed adjacent to the tissue; displacing the electrode a predetermined increment, wherein the predetermined increment is determined based upon one or more of the dimensions of the electrode; and repeating the above steps one or more times to create a continuous lesion.